Garda headquarters is bracing itself for an exodus among its highest ranking members ahead of Public Expenditure Minister Brendan Howlin's plans to slash public sector pension payments.

The Sunday Independent understands there is growing concern among Garda management that hundreds of experienced officers will retire en masse to avoid losing out on thousands of euros in pension payments.

Sources claim senior officers could be down as much as €7,000 a year if they do not quit the force before next summer. A grace period on public sector salary cuts, which also affect pensions, will end in June 2015.

"They could all down tools and put in their papers next summer," a source said. "The last thing the gardai need is a mass exodus. If all those people left next year it would have serious implications."

The Sunday Independent understands all 12 of the force's assistant commissioners are eligible for retirement with full entitlements, as are 37 chief superintendents and 104 superintendents. In the inspector ranks, 145 officers are also able to leave next summer and avail of more lucrative pension payments.

A further 448 garda sergeants and 660 rank-and-file gardai are eligible for retirement next year, but because they earn less than €65,000 a year they did not receive salary cuts under the Haddington Road Agreement.

The possible appointment of a Garda Commissioner from outside the force and low morale following the whistleblower scandals are viewed as additional factors which may lead to early retirement among the senior ranks.

The appointment of a Commissioner from a different country or profession would automatically limit promotional opportunities for assistant commissioners. A career break scheme offering gardai €35,000 to take three years off duty has also resulted in manpower problems.

There are also fears in Garda headquarters that the Department of Justice will not follow through on its commitment to make funding available for 300 new recruits this year. Some 100 cadets will begin training in Templemore Garda College over the coming weeks, but the department has yet to sign off on funding for the remaining 200 officers promised last year.

A Justice department spokesman said a review of the gardai, which is part of the Haddington Road Agreement, will determine how much additional resources are made available.

"While it is fully expected that additional gardai will be recruited later this year and into the future, the precise numbers involved will be determined by Government," he said.

In December 2013, former Justice Minister Alan Shatter announced 300 gardai would be recruited by the end of this year. It was envisaged 100 would be training by July and the rest would be recruited by the end of the year. More than 20,000 people have applied to join the force since the recruitment process was announced.

Sources say gardai could "fill Templemore in the morning" if funding was made available. A recruitment freeze has been in place across the public sector since 2009. In the same year, almost 600 gardai retired or applied to leave the force when the Government introduced the pension levy.

Last year, pension lump sums for 335 retired garda cost the State €30m and included a payout of more than €170,000 for one senior garda. The previous year, 462 gardai received €42m, while 480 retiring gardai received €46m in pension lump sums in 2011.

Former Garda Commissioner Martin Callinan, who stepped down in May in the midst of the Garda scandals, is entitled to an estimated €85,000 pension. He also reportedly received a €255,000 lump sum when he stepped down.

A garda must be 50 or older with 30 years service to retire with a full public service pension. All public sector workers, who have more than 30 years' service, receives a pension lump sum based on one-and-a -half times their salary.

Every year after, they receive half their final salary as an annual pension payment. Public sector workers, including gardai, who earn more than €65,000 received pay cuts under the Haddington Road Agreement.

The salary cut would also affect a worker's pension payments as their salary on retirement would ultimately be reduced.

However, when the pay deal was agreed with unions, the Government introduced a grace period which allowed workers receive pension lump sums and yearly payments based on their salary before the pay cut.

The deadline for pensions calculated at previous rates was due to end this month. However, earlier this year Mr Howlin announced an extension of the grace period until June 2015.

Unions have warned the minister that once the salary cuts are applied to pensions there will be serious consequences for staffing levels across the public sector.